1. Field of the Invention
The present invention relates to a system for controlling traveling movements of a self-moving vehicle.
2. Description of the Related Art
A self-moving vehicle, in general, has a driving wheel on each lateral side. Each driving wheel is driven in rotation by a respective motor. The travel control of such a self-moving vehicle is accomplished by controlling the rotation of the motors to maintain a constant travel direction or course of the vehicle.
Some of the conventional travel control systems for self-moving vehicles are disclosed in Japanese Patent Appln. Laid-Open No. 63-241611 and Japanese Patent Appln. Laid-Open No. 64-10613. In these systems, the traveling direction of the vehicle is detected with a gyro. Corrections of the direction are performed by steering to maintain an instructed direction by comparing the actual traveling direction with the instructed direction.
An error can be produced in an output signal from the gyro by an integration error, or a voltage drift in a circuit, when the gyro is used as a direction sensor. The error has a tendency to increase with elapse of time, being influenced by integration. Therefore, there has been a problem that it becomes impossible to detect accurately the actual traveling direction of the vehicle. Consequently, the actual traveling direction may deviate from the instructed direction.
An apparatus for controlling the travel of the vehicle without using the gyro is disclosed in Japanese Patent Appln. Laid-Open No. 3-6606. In the apparatus, the actual rotational displacements are compared with the rotational displacements to be made by the driving wheels on both sides for a predetermined period of time. Then the traveling direction is controlled by controlling the motors on both sides which are provided for respective driving wheels based on the deviation between the two wheels.
It is found that the feedback control of a motor system based on the rotational displacement of a motor is not able to cope with the trouble, when a rotational displacement is large, as in a case of a slip between a tire and a road surface.
As described above, there have been problems in a conventional travel control system for a vehicle. That is, when the gyro is used, the traveling direction of the vehicle gradually deviates. When the feedback control of the motor system is used, the feedback control becomes unable to cope with trouble such as tire slippage.